I agree. A rx is set up on a paralell bus system. You could put 4 different packs on a rx and all it will do is increase your Mah(mili-amp hours). This will only increase you flight time and your weight[&o] and in 3d, wt is the enemy... If you want more speed and torque, go with the 5 cell pack as Gordo stated. Also, some servos will not take a 5cell=6vdc load. Find out your servo specs before you fry one...better safe than poor......
My 2 cents,
Shane